To begin, filamentous algae is easily recognizable, but are you positive that your weed problem is coontail and not some other weed species? Coontail is a plant with no true roots, thus most of it grows as weed masses hanging in the water column and not attached to the bottom. Regardless your pond has a lot of it.
Your pond is once again proof that aeration, even very good aeration, will not overpower the effects of heavy nutrient enrichment and weeds that include filamentous algae and submerged weeds. IMO your pond should be "poster boy" for people who think or are told that aeration will solve all their algae problems.
https://maps.google.com/maps?q=260+SE+58...ved=0CCkQ8gEwAA Often in situations where nutrient concentrations are "on the fence" between low and mild (early or middle age pond), aeration can appear to be a significant deterrent to algae problems. And in these instances is where the whole idea of aeration controlling plants (algae) 'sprouted', although IMO it is an erroneous concept. Push the nutrients to the next higher level and the best aeration fails. Then supplemental management efforts such as dyes, algaecides, bacterial (microbe) additions, submerged rooted plants, and a few other natural methods are needed to keep the pond from being overgrown with nuisance plants. Accumulation of even more nutrients requires more and more of the previous abatements until when using all those combined seem to have little impact on the rampant growth of plants.
Eliminate one nuisance and another form appears. 'Mother Nature' demands that something will grow in the over enriched, hyper-eutrophic, nutrient 'soup bowl' called a pond. Duck weed and watermeal are two plant indicators of over enriched conditions. In these situations not much seems to work or 'clean things up' at least for very long.
I do not relish sounding negative, but laws of Mother Nature are often not kind nor politically correct.
Regarding the floating islands and if they will be effective, Have you spoken with Bruce Kania at Floating Islands International (FII) about the necessary amount or surface area of FI that are needed per acre to abate your nutrient soup pond? Have you conducted any nutrient tests to determine the amount of nutrients that need to be absorbed, processed, or sequestered each year? I think for FI to work effectively, one needs to know how many nutrients available need to be sequestered and then use the appropriate amount of FI sq footage to get the job accomplished. I am sure that it is known by FII approximately what each sq ft of FI can accomplish in nutrient sequester per growing season. I suspect from seeing the amount of plant growth in the picture above that the cost for the adequate amount of FI will be quite high.
Considering what you have spent in time and manual "LABOR" to date for plant control and what you will spend in the near future my advice is to plan in the near term a pond renovation where elimination of sewage discharges and thick nutrient bottom sludge will make a world of difference in the amount of annual nuisance plant growth. Aeration investment is usable in any age of pond, new, renovated or old. Other investments such as bacteria and chemicals, etc. are lost and not good long term investments since they are temporary fixes.
Ponds are catchment basins, especially those that are sediment traps with high nutrient inputs and have minimal flushing (long retention times). As soon as ponds/lakes are excavated and filled with water, Mother Nature's plan is to fill them back up with muck and sloppy sediments until they are a swamp and then back to dry land. It is called aquatic succession. We pond owners try as much as possible to slow and delay that process. In situations where poor design and poor or no management prevails, the aquatic succession happens fairly quickly due to high nutrient inputs and excessive annual plant growth. Thus a pond such as this one, built relatively recently as a nutrient accumulator and enriched sink are after a fairly short time over enriched and a plant infested mess for lack of a better term.
There are no magic bullets to my knowledge (wish there were) for a pond in the current condition. I doubt that you will get any guarantees for any of your "pond fix" investments. For your long term plan, I suggest that you investigate prices or bids for good, skilled, wisely planned, pond renovation for your situation. A renovated pond does not have to be as big as the current pond. Spoils from rebuilding can be stored in some of the current bottom areas thus rebuilding does not have be as expensive as building an entire current size. Get that body of water back to new condition with wise nutrient, watershed management, that at the end, includes bottom aeration and then you will have a lot fewer headaches, less aggravation and fewer sore mussels. Then you will have an enjoyable water resource instead of a continual low water quality, plant infested problem.
